JPH06333525A - Charged particle beam irradiation device - Google Patents

Abstract

PURPOSE:To improve the performance and the service life of a charged particle beam source by providing the first aperture, and a lens to fix the focus at the hole of the aperture, at the outlet of a chamber to house the charged particle beam source. CONSTITUTION:The particle beams of electron beams 23 discharged from a cathode 1 are focused by a solenoid lens 21 provided at the outlet of a chamber 4, and the focus is fixed to the surface of an aperture 20. In this case, by increasing or decreasing the excitation of a deflection device 22, the focus of the beams at the surface of the aperture 20 can be made coincident to the position of the hole of an adequate size. And the aperture 20 held by an insulator 28 is connected to a current detecting device, and the current generated by hitting the beams to the aperture 20 is detected. As a result, it is decided whether the focus position is coincident to the hole of the aperture 20 or not. By such a constitution, the charged particles are not hit to the chamber 4 to house the beam source, or to the aperture 20, and the performance and the service life of the beam source are improved extensively.

Description

Detailed Description of the Invention

[0001] [Industrial field of application] The present invention provides a means for preventing a particle beam from colliding with a chamber, an aperture, or the like that accommodates a charged particle beam source, and for reducing gas inflow into the chamber. The present invention relates to a charged particle beam irradiation apparatus in which adsorption of gas to a radiation source and attack of ions are reduced, and as a result, performance and life of the radiation source are improved. [Prior Art] In a charged particle beam irradiation apparatus such as an electron microscope, an electron beam exposure apparatus, an electron beam processing apparatus, an electron beam welding apparatus, and a focused ion beam apparatus, a charged particle beam is generated and irradiated. An irradiation system is provided. As an example, FIG. 3 shows an irradiation system of a scanning electron microscope using a thermal electron gun. In the figure, 1 is a cathode, 2 is a Wehnelt, and 3 is an anode (anode), and these together form an electron gun. An electron gun chamber 4 is exhausted by an exhaust device 5. 6 is an electromagnetic condenser lens, 7 is an electromagnetic objective lens, 8 and 9 are apertures, 10 is a liner tube, 11 is a sample, 1
Reference numeral 2 is a sample chamber, and the liner tube and the sample chamber are exhausted by exhaust devices 13 and 14, respectively. The outer peripheral portion of the electron beam 15 emitted from the cathode collides with the aperture 8 and is blocked, and the central portion passes through the aperture and is focused by the condenser lens 6. Further, the electron beam is similarly focused by the objective lens 7 and irradiated on the sample 11. Further, the electron beam is scanned over the sample by a scanning coil (not shown), at which time secondary electrons are generated from the sample, and these are detected by a detector (not shown) to form an electron microscope image. [0004] [Problems to be Solved by the Invention] In such a conventional electron microscope, an electron beam generated from an electron gun collides with an aperture 8 or a chamber 4, and at this time, a gas is emitted from the surface of the aperture or the chamber. And generate ions.
As a result, the pressure in the chamber rises, the gas is adsorbed on the cathode, and the ions attack the cathode, which change the physical properties and shape of the cathode and deteriorate the characteristics and life of the cathode. [0005] A further problem is the inflow of gas from the liner tube. Generally, the vacuum pressure in the liner tube is high, so that gas flows from the liner tube into the electron gun chamber to deteriorate the degree of vacuum. In order to prevent this, it is desired that the hole diameter of the aperture 8 is as small as possible, but on the other hand, a certain hole diameter is necessary to extract the required electron beam amount downward, and it is usually 0 in an electron microscope or the like. About 0.3 to 0.5 mm is used. With such an aperture diameter, the gas inflow reaches a considerable amount,
It raises the pressure in the electron gun chamber and degrades the cathode characteristics and life. [0006] Since an electron beam exposure apparatus, an electron beam processing apparatus, an electron beam welding apparatus, etc. draws a larger current, the aperture hole diameter is 0.5 to 8 mm.
Degree is required, in which case the effect of gas inflow is more serious. Further, the field emission type electron gun used in a high resolution electron microscope or the like has the same problem because its characteristics and life are deteriorated even by slight gas adsorption or ion attack. As described above, the problems such as gas adsorption, ion attack, and gas inflow are serious in various devices, and it is desired to solve them. However, there is no sufficiently effective means in the prior art, and therefore, it is a great disadvantage in practical use. Was coming. [Means for Solving the Problems] According to the present invention, a first aperture is provided at the exit of a chamber that houses a charged particle beam source, and the particle beam is focused to focus on the surface of the aperture. It has a lens that makes it. Further, there are provided adjusting means for matching the focus position with the hole of the aperture and means for determining that they match. [Operation] By the above-mentioned means, all of the particle beam passes through the aperture without colliding with the aperture or the chamber. In addition, the hole diameter of the aperture is made small to reduce the inflow of gas into the chamber. As a result, the degree of vacuum of the chamber is improved, the adsorption of gas to the radiation source and the attack of ions are reduced, and the performance and life of the radiation source are improved.

[Embodiment] FIG. 1 is a first embodiment of the present invention and shows an irradiation system of a scanning electron microscope using a thermionic gun. In this figure, the components denoted by the same reference numerals as those in FIG. 3 are the same components. The cathode 1 is usually a tungsten filament,
Lanthanum hexaboride or the like is used. A first aperture 20 is provided at the exit of the electron gun chamber 4. After that, the apertures 8 and 9 are provided as in the conventional example. The aperture 20 is supported by being insulated from the ground by an insulator 28, and is electrically connected to a current detecting device (not shown). Reference numeral 21 is an electromagnetic lens, and 22 is an electromagnetic deflection device. [0010] The electron beam 23 emitted from the cathode spreads in a conical shape, is focused by the lens 21, and focuses on the surface of the aperture 20. The hole diameter of the aperture is selected to be slightly larger than the diameter of the focal point of the beam, and in the present embodiment, it is about 30 to 100 μm. Deflection device 22
By adjusting the position of the focal point of the beam on the aperture plane by increasing or decreasing the energization of the beam, and making the position of the focal point coincide with the hole of the aperture, all the beams pass through the aperture. [0011] As described above, the aperture 20 is connected to the current detecting device. When the beam hits the aperture, the current absorbed by the aperture is detected by the detector, and when the beam is passing through the aperture, the detected current is almost zero. It can be determined that the positions of the holes in the aperture match. The beam that has passed through the aperture is focused by the condenser lens 6, and thereafter, the beam shown in FIG.
The description is omitted because it is the same as the conventional example. [0012] As described above, the electron beam does not collide with the chamber 4 and the aperture 20, and therefore, gas, ions and the like are not generated on the surface thereof. Further, since the hole of the aperture 20 may have a small diameter slightly larger than the focal point of the beam, the gas inflow from the liner tube into the electron gun chamber becomes negligibly small.
As described above, since the aperture hole diameter of this embodiment can be set to about 30 μm, if the diameter of the conventional device is 0.3 mm, the gas inflow amount is reduced to about 1/100. Therefore, by exhausting with the exhaust device 5, it is possible to reach a sufficiently high vacuum. The deflector 22 is not always necessary. If the electron gun, lens, aperture, etc. are manufactured and assembled with good axial accuracy, the beam focus passes through the aperture without the deflector. In this case, the insulation support by 28 and the detection of the absorption current of the aperture are naturally unnecessary. Further, as a means for adjusting the position of the beam, an axis aligning device for mechanically moving the electron gun may be provided instead of the deflecting device. [0014] Fig. 2 shows a second embodiment of the present invention, showing an electron irradiation system using a field emission type electron gun. In this figure, the components denoted by the same reference numerals as those in FIG. 1 are the same components. Reference numeral 25 is an emitter, and a needle-shaped tungsten single crystal or the like is used at the tip thereof, and electrons are emitted from it. 26 is a first anode, the lower surface of which forms the first aperture 20. The first anode is held by an insulator 28 and is connected to a current detection device and a high voltage power source (not shown). Different high voltage potentials are applied to the emitter and the first anode from the outside, a strong electric field is formed on the front surface of the emitter due to the potential difference between the two, and the electron beam 23 is field-emitted. The emitted electron beam is focused by the lens 21 and focused on the surface of the aperture 20. Since the diameter of the focal point is extremely small in the case of the field emission electron gun, the hole diameter of the aperture may be about 10 μm. If the position of the focal point on the aperture plane is adjusted by the deflecting device 22 so that the position of the focal point coincides with the hole of the aperture, the beam passes through the hole of the aperture. Reference numeral 29 is a second anode, the hole diameter of which is selected to be about 1 to 5 mm, and it is electrically grounded. The beam passing through the second anode is focused by the condenser lens 6, and the rest is the same as in FIG. [0016] Also in this embodiment, the electron beam does not collide with the chamber 4, the first anode 26, and the aperture 20, and therefore, gas, ions, etc. are not generated on the surface thereof. Further, since the amount of gas flowing into the electron gun chamber through the aperture is so small as to be negligible, it is possible to exhaust the gas to an ultrahigh vacuum by the exhaust device 5. Therefore, the problem that the field emission type electron gun deteriorates in its characteristics and life due to slight gas adsorption or ion attack is solved, and the electron gun can be operated stably. [0017] In the field emission type electron gun, different potentials are applied to the first anode and the second anode,
Therefore, an electric field exists between the two, and the electrons are accelerated or decelerated there to reach the final energy, but this electric field forms an electrostatic lens, and in general, the electrostatic lens has an aberration. Since it is large, there is a problem that this deteriorates the performance of the irradiation system. However, in this embodiment, since the beam is focused near the electric field (that is, the electrostatic lens), the focusing action of the electrostatic lens is hardly received, and therefore, the adverse effect on the irradiation system can be extremely small. This is a further effect of the present invention. Although the present invention has been described with reference to the embodiment of the electron gun, the present invention can be implemented with a similar configuration in an ion beam irradiation system using an ion gun. However, in that case, an electrostatic lens is used as the lens. In the case of an ion gun, there is no problem of ion attack, so there is no effect on this, but other effects can be used. As described above, the present invention can be applied to an irradiation system of a charged particle beam such as electrons and ions. [Effect of the Invention] Since the present invention is configured as described above, the charged particle beam does not collide with the chamber or the aperture that houses the radiation source, and the gas does not flow into the chamber. Reduced to a negligible level. As a result, the chamber is evacuated to a sufficiently high vacuum, the adsorption of gas on the source and the attack of ions are reduced, and the performance and life of the source are greatly improved. Further, in the field emission type electron gun, the influence of the aberration due to the electrostatic lens formed in the vicinity of the anode can be kept extremely small.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example in which the present invention is applied to an irradiation system using a thermionic gun. FIG. 2 is a sectional view showing an example in which the present invention is applied to an irradiation system using a field emission electron gun. FIG. 3 is a cross-sectional view showing an irradiation system using a thermal electron gun according to a conventional technique. [Explanation of Codes] 1 Cathode 2 Wehnelt 3 Anode 4 Chamber 5 Exhaust device 20 Aperture 21 Lens 22 Deflector 23 Electron beam 25 Emitter 26 First anode 28 Insulator 29 Second anode

Claims (2)

[Claims] [Claim 1] A charged particle beam source, a chamber for accommodating the charged particle beam source, and an exhaust device for evacuating the chamber are provided, a first aperture is provided at an outlet of the chamber, and a focus of the charged particle beam is provided on the aperture surface. A charged particle beam irradiation device characterized in that a lens that can be connected to is provided. [Claim 2] The charged particle beam irradiation apparatus according to claim 1, further comprising means for adjusting the position of the focal point of the charged particle beam on the aperture surface and means for detecting the current absorbed by the aperture.